Generating Terahertz (THz) radiation in the frequency range from 0.1 to 10 THz is the next frontier in imaging science and technology. THz radiation finds its way into applications ranging from medical imaging, counter terrorism and homeland security, to land mine detection. It is highly desirable to use THz radiation sources for the abovementioned applications because THz radiation is non-ionizing, penetrates plastic, concrete and other common materials and can be used to recognize and identify biological agents and explosives. The wide-range of applications for THz radiation has not been widely developed because there has been a lack of flexible and affordable THz sources or generators. For example, there is an absence of robust THz generators or sources of practical or transportable size.
THz radiation generation has been achieved using several different technologies, none of which presently spans the full range of wavelengths or matches all performance requirements. Techniques for generating THz radiation span a wide range of devices encompassing laser driven semiconductor switches, optically pumped carbon dioxide (FIR) lasers, and electron beam devices, which include mainly backward wave oscillators (BWO) and their variants, Smith-Purcell (grating) devices, gyrotons, conventional free electron lasers (FELs), and synchrotron radiation sources. Most of these devices, however, have been able to generate THz radiation in the power range of only a few milliwatts (mW), more typically 10's of microwatts (μW) with no clear path for scaling to higher power. For many applications, this range of power is insufficient. For example, radar applications, long range secure communications, photon-assisted chemical reactions, certain biomedical applications, and wide field-of-view (FOV) imaging and stand-off detection may require more power.
Increasing peak and average power of THz generation has become more promising with regard to some electron beam devices. Electron beam devices such as FELs and synchrotron radiation sources have demonstrated good potential as high power THz sources. However, these devices have problems with respect to size, cost, and radiation safety. Consequently, known techniques for generating THz radiation are unsatisfactory in certain situations.